Edmundo Díaz-Pardo

Patterns in the distribution of fish assemblages in Río Amacuzac, Mexico: influence of abiotic factors and biotic factors

Patterns in spatial and seasonal distribution of fish communities were analyzed in the Río Amacuzac, Mexico, and their relationship to environmental variables and habitat characteristics. The PCA biplot of the study sites and environmental factors showed the first two axes accounting for 52.93% of the variance. The diagram showed the study sites ordination in environmental gradients. The first axis explained variables related to habitat characteristics and temperature (36.30%) and second axis arranged the sites in physicochemical and water quality environmental gradients (conductivity, dissolved oxygen, orthophosphates, ammonium, pH) displaying seasonal variation. Fifteen species were recorded, eight of them are exotic. One new record appeared for the Río Amacuzac: Pterygoplichthys disjunctivus is exotic. Study sites with highest species richness were: 5, 7 and 9 (twelve species each one); while the study sites with low species richness were 1, 2, 3 and 6 (eight species each one). Six of the species were distributed throughout the whole river. Based on the composition of the fish fauna, the study sites form two groups and the analysis of fish species displays three groups according to the Bray–Curtis index. The diagram of the canonical correspondence analysis relates environmental parameters to the abundance of fish species and showed that the first two axes exhibit 78.31% of the explained variance. Species richness had a spatial pattern associated to the introduction of exotic species for ornamental uses. According to the results of the importance value index (IVI), the dominant species were the poecilids Poeciliopsis gracilis and Heterandria bimaculata, small fishes that were introduced in the river. Río Amacuzac has a biotic alteration in the structure of fish communities due to the invasion of exotic species, representing risks to the integrity of the native fish fauna.

Diferencias Osteológicas entre los Subgéneros Profundulus y Tlaloc (Teleostei: Profundulidae)

El genero Profundulus es uno de los grupos de peces mas antiguos, distribuidos al norte de America Central en Mexico, Guatemala y Honduras. No obstante, son pocos los trabajos que se han realizado para conocer el numero de especies que lo conforman y sus relaciones filogeneticas. Historicamente se reconocio que este taxon estaba conformado por dos grupos naturales, actualmente considerados como los subgeneros Profundulus y Tlaloc. Recientes investigaciones geneticas han revelado un alto grado de diferenciacion entre ambos taxones y algunas de sus especies, lo cual probablemente este asociado a cambios morfologicos. De esta manera, se realizo la comparacion osteologica entre seis especies de los subgeneros Profundulus y Tlaloc (Cyprinodontidae: Profundulidae). Se revisaron 17 huesos ubicados en el craneo y la cintura pelvica, se encontraron diferencias cualitativas en el mesetmoides, vomer, lacrimal, premaxilar, articular, cuadrado, interoperculo y basipterigio. Los patrones de variacion observados permiten diagnosticar ambos subgeneros, corroborando lo encontrado en estudios morfologicos y moleculares. Las evidencias permiten suponer que ambos taxones podrian ser reubicados como generos, como previamente se habia establecido.